An important quality for a vehicle of this nature is its ability to move over rough ground, i.e., ground having obstacles to be overcome. Obstacles can arise in a wide variety of forms, for example a staircase designed for humans and which must be gone up or down, or a pipe that has fallen on a floor. There are two main aspects to the safety of such vehicles when they are overcoming such obstacles. One of them is stability, i.e., the ability of the vehicle to avoid toppling over under its own weight and the weight of its load. The other problem is adherence, and this applies to each of the vehicle propulsion units, i.e. the members of the vehicle that bear against the ground for supporting the vehicle and for causing it to move or stand still. Adherence relates to the ability of these propulsion units to avoid slipping excessively on contact with the ground, even when the surface state of the ground is locally unfavorable.
Another important quality of such a vehicle is its size, in particular its transverse and longitudinal dimensions, which must be small enough to enable the vehicle to travel along various passages or corridors inside buildings that were designed for people only.
Another important quality is that the vehicle should be as light as possible.
Various vehicles have been designed for overcoming obstacles safety. A first vehicle is disclosed in ACEC's EP 197 020 which describes a remotely controlled vehicle constituting a robot for performing inspections and interventions in hostile environments. The vehicle has a drive assembly, i.e., means for applying drive and braking, which assembly is integrated in a main chassis of the vehicle. It also possesses means for transmitting the forward drive defined by said drive assembly to crawler tracks carried outside the chassis on propulsion units themselves carried by the vehicle. The vehicle is fitted with two propulsion units, one at the front and the other at the back, each of the propulsion units having two tracks mounted thereon, one on the left and the other on the right. Each propulsion unit may be tilted relative to the vehicle from the vehicle. Thus, if the robot encounters an obstacle head on, and the obstacle is of a moderate height that is substantially constant in the transverse direction, then the vehicle can pass over the obstacle while maintaining the vehicle body in a substantially horizontal position. However, if the vehicle encounters a head-on obstacle that slopes steeply sideways, then it runs the risk of toppling over sideways as it climbs over the obstacle.
A second known vehicle moves by means of legs in a "spider" type configuration, thereby enabling it to overcome a very wide variety of small obstacles. However, it moves very slowly because it is not possible, in general, to move a plurality of the vehicle's legs simultaneously.
A third known vehicle has four crawler-track propulsion units each capable of being tilted relative to the body of the vehicle. The crawler track of each propulsion unit is guided over a certain number of guide members, in particular over two wheels, one of which is a drive wheel for causing the crawler track to move forwards. These members are carried by a housing which constitutes the structure of the propulsion unit and which is assembled to the body of the vehicle in such a manner as to enable the propulsion unit to be tilted about a transverse axis. The vehicle body carries drive assemblies including motors both for tilting and for forward motion, some of which assemblies drive the drive wheels via mechanical transmission systems and others of which drive the tilting movements of the propulsion units. These assemblies also include brakes for controlling movement. The vehicle body also carries electrical power supply batteries and means for controlling the drive assemblies.
This third known vehicle is proposed by the Mitsubishi under the name MRV (Multifunctional Robot Vehicle), and is described at pages 425 and 426 in the proceedings of the "85 ICAR International Conference on Advanced Robotics", Sept. 9-10, 1985, Tokyo, Japan, organized by the Robotics Society of Japan, The Society of Biomechanisms, and the Japan Industrial Robot Association. It appears to be capable of overcoming obstacles of known shapes, and it seems to be capable of a forward speed considerably higher than that of the above-mentioned second known vehicle. Nevertheless, it appears to present the above-mentioned important qualities to an insufficient extent only.
European patent application EP-A-0 206 930 describes a fourth known vehicle comprising two pairs of propulsion units, one at the front and the other at the back, these pairs of propulsion units being carried by front and back portions of the vehicle body and each of them being constituted by two crawler track propulsion units, one on the right and the other on the left. Each propulsion unit has two wheels, a front wheel and a back wheel, a crawler track which is supported by and driven by said wheels, and track support means between the two wheels.
This known vehicle is of variable configuration or geometry, in the sense that the front and back portions of the vehicle body are hinged relative to each other about a middle transverse axis. This axis coincides with the axis of the rear wheels in the front pair of propulsion units and with the axis of the front wheels in the back pair of propulsion units.
It is disclosed that obstacles can be overcome without compromising the stability of the vehicle by displacing its center of gravity and by altering the realtive angular position of the two portions of the vehicle body.
Although this known vehicle does indeed appear to be capable of overcoming obstacles without losing stability, this capability appears to be somewhat limited.